Anatomy in relation to taxonomy by venkat parker

Anatomy in relation to taxonomy by venkat parker

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  M.Venkatesh. I M.Sc Botany
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  INTRODUCTION  Anatomical featureshave played an increasingly important role in elucidation of phylogenetic relationships .  Anatomical characteristics are investigated with the help of a light microscope where as ultra structure and micromorphology are brought out using an electron microscope.  Anatomical work of taxonomic significance was largely under taken by Bailey and his students.
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  WOOD ANATOMY Wood representssecondary xylem constituting the bulk of trees and shrubs formed through the activity of vascular cambium . It primarily consists of tracheids and vessels . Tracheids are long narrow elements with tapering ends, it transfer of water and minerals occuring through pit-pairs. Vessel elements are joined end to end to form long tubes the vessels Vessels are absent in gymnosperms but present in angiosperms.
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  The separation ofPaeonia into a distinct family Paeoniaceae and Austrobaileya into a separate family Austrobaileyaceae has been supported by studies of wood anatomy. Nodal anatomy has considerable significance in angiosperm systematics. The node may have single gap from single leaf trace is called as unilacunar. The node is three leaf traces or three gaps is called as trilacunar.
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  TRICHOMES Trichomes constitute appentagesof epidermis which may be non-glandular or glandular. Non glandular trichomes may be in the form of simple unicellular or multicellular hairs common in Brassicaceae, Lauraceae. Glandular trichomes may be sessile or stalked and present a variety of forms.
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  EPIDERMAL FEATURES o Epidermalfeatures are also of considerable taxonomic interest. o Prat (1960) demonstrated that one can distinguish a festucoid type (simple silica cells, no bicellular hairs) and panicoid type (complicated silica cells, bicellular hairs ) of epidermis in grasses. o Stomatal types are distinctive of certain families such as Ranunculaceae (anomocytic) Brassicaceae (anisocytic) Caryophyllaceae (diacytic) Rubiaceae (paracytic) and poaceae (graminaceous).
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  o Stace (1989)lists 35 types of stomata in vascular plants. o Closely related families Acanthaceae and Scorpulariaceae are distinguished by the presence of diacytic stomata in the former as against anomycytic in the latter.
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  LEAF ANATOMY  Leafanatomy has been of special taxonomic help in Poaceae family.  The occurance of c-4 path way and its association with Kranz anatomy  Melville(1962,1983) developed his gonophyll theory largely on the basis of the study of venation pattern of leaves and floral parts.  The rejection of Sanmiguelia and Furcuta as angiosperm fossil from the triassic has largely been on the basis of detailed study of the venation pattern of leaves.
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  FLORAL ANATOMY  Floralanatomy has been one of thoroughly explored areas , with singnificant contributions to the understanding of the phylogeny of angiosperms.  Melvile (1962, 1983) developed his gonophyll theory after studing the vasculature of carpel and other floral parts through the clearing technique.  The inferior ovary in angiosperms has been formed in two ways : appendicular origin or by axial invagination.
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   Floral anatomyalso supports the seperation of Menyanthes from Gentianaceae into distinct family Menyanthaceae.  Developmental studies have indicated that some flowers, such as Apiaceae and Ericaceae that appear to have free petals, are gamopetalous early in development.  They are therefore considered to have evolved from gamopetalous ancestors.
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  EXAMPLE:1 Aizoaceae  Mollugo  Trianthema Sesuvium  Gisekia Aizoaceae Aizoaceae Molluginaceae  Trianthema Mollugo  Sesuvium  Gisekia
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  Anatomy plays ina major role of ‘P’and ‘S’ plastids o It is proposed by Hutchinson. o Phloem consists of the following elements a)Sieve tubes b)Companion cells c)Phloem fibre d)Phloem parenchyma
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  Companion cells containtwo types of plastids ‘P’ Plastids ‘S’ Plastids P means of Protein bodies. S means of Starch granules. Aizoaceae is the presence of ‘P’ Plastids. Molluginaceae is the presence of ‘S’ Plastids.
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  o Phloem consistsof the following elements a)Sieve elements b)Companion cells c)Phloem fiber d)Phloem parenchyma
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  Floral anatomy alsosupports the separation of Menyanthes from Gentianaceae into distinct family Menyanthaceae. EXAMPLE: 2 Gentianaceae Centella Hydrocotyle Gentianaceae Gentianaceae Menyanthaceae Centella Hydrocotyle 
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  EXAMPLE: 3 Ranunculaceae: Ranunculus Thalictrum Delphinium Aquilegia Ranunculaceae Ranunculaceae Helleboraceae RanunculusDelphinium Thalictrum Aquilegia 
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  Reference book:  PlantTaxonomy by O. P. Sharma  Systematic Botany by Guru Sharan Singh  Plant Anatomy by M.S.Tayal  12th Standard Botany Book